Process for the selective hydrogenation of pyrolysis gasoline

ABSTRACT

HYDROGENATION OF PYROLYSIS GASOLINES OR FRACTIONS THEREOF IN A FIRST STEP AT A TEMPERATURE BELOW ABOUT 100* C. TO HYDROGENATE SELECTIVELY SUBSTANTIALLY THE DIOLEFIN CONTENT THEREIN, AND THEREAFTER IN A SECOND STEP OF THE HYDROCARBON MIXTURE OBTAINED FROM THE FIRST STEP AT A TEMPERATURE ABOVE 100*C., E.G. AT ABOUT 150-250*C., TO HYDROGENATE SELECTIVELY SUBSTANTIALLY THE MONO-OLEFIN CONTENT THEREIN, BOTH STEPS USING NOBLE METAL ON AN ALUMINUM SPINEL SUPPORT AS HYDROGENATION CATALYST, AT A HYDROGEN PRESSURE OF ABOUT 20-80 ATMOSPHERES, PREFERABLEY IN A SUBSTANTIALLY STATIC HYDROGEN ATMOSPHERE, AND OPTIONALLY WITH RECYCLING OF HYDROGENATION PRODUCT TO THE HYDROGENATION REACTOR.

United States Patent 3,556,983 PROCESS FOR THE SELECTIVE HYDROGEN ATION F PYROLYSIS GASOLINE Walter Kronig, Leverkusen, and Kurt Halcour, Cologne- Stammheim, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany No Drawing. Filed Oct. 15, 1968, Ser. No. 767,811 Claims priority, application Germany, Oct. 19, 1967, 1,645,747 Int. Cl. C10g 23/04 US. Cl. 208-27 11 Claims ABSTRACT OF THE DISCLOSURE Hydrogenation of pyrolysis gasolines or fractions thereof in a first step at a temperature below about 100 C. to hydrogenate selectively substantially the diolefin content therein, and thereafter in a second step of the hydrocarbon mixture obtained from the first step at a temperature above 100 C., eg at about ISO-250 C., to hydrogenate selectively substantially the mono-olefin content therein, both steps using noble metal on an aluminum spinel support as hydrogenation catalyst, at a hydrogen pressure of about 2080 atmospheres, preferably in a substantially static hydrogen atmosphere, and optionally with recycling of hydrogenation product to the hydrogenation reactor.

This invention relates to a process for the selective hydrogenation of pyrolysis gasoline.

It has been found that pyrolysis gasoline or fractions thereof can be selectively hydrogenated with good results by hydrogenating pyrolysis gasoline or fractions thereof first at temperatures below 100 C. in the presence of noble metal catalysts on aluminum spinel supports in order selectively to hydrogenate mainly the diolefins, followed by hydrogenating the greater part of the monoolefins in the hydrocarbon mixture thus obtained at temperatures of from 150 to 250 C., using noble metals on aluminum spinel supports as hydrogenation catalysts.

The same noble metal catalyst on spinel supports may be used for both hydrogenation stages, below and above 100 C., in the process according to the invention. It has proved advantageous to carry out the hydrogenation above 100 C. immediately after the hydrogenation below 100 C. in the same reactor and at the same pressure.

It is of advantage to operate in the trickle-phase throughout the reaction zone in a substantially not moving, i.e. static or quiescent, hydrogen atmosphere.

Suitable starting materials include highly unsaturated gasolines, so-called cracked gasolines, obtained in the pyrolysis of liquid hydrocarbons. These cracked gasolines are with advantage subjected to a redistillation before they are used for hydrogenation in order thus to separate off those constituents whose boiling points lie above the boiling range of gasoline. In this redistillation in which steam is advantageously fed in, for example in proportions of from 2 to 10 parts by weight of steam to 100 parts by weight of pyrolysis gasoline, the distillation range is best arranged in such a way that the redistillate has a gum content of less than 5 mg./100 ml. of gasoline. It has proved advantageous to add an ageing inhibitor to the distillate, for which purpose the inhibitors used for motor gasoline, preferably the phenolic inhibitors, are suitable, for example di-tert.-butylphenol, in quantities of from about 20 to 100 ppm. Since there is no increase in the gum content where hydrogenation is canied out by the Patented Jan. 19, 1971 process according to the invention, the product of hydrogenation does not have to be subjected to redistillation. The starting materials normally have bromine numbers of from 50 to g/ g and diene contents of from 8 to 25%. Instead of using the total redistilled cracked gasoline, it is also possible to use fractions thereof for hydrogenation, for example certain aromatic fractions such as the BT fraction (benzene-toluene fraction) or the BTX fraction( benzene-toluene-xylene fraction).

Noble metals on supports are used as the hydrogenation catalysts. Suitable noble metals include in particular palladium and mixtures of palladium with other noble metals such as platinum, ruthenium, gold and others, and with other additives. Supports containing aluminum spinel are used to support the noble metal. Average pore diameters in the catalyst supports of from 200 to 800 A. and inner surfaces of from 20 to m. /g., have proved to be suitable. The supports containing aluminium spinel may be obtained for example by heating aluminium oxide with spinel-forming compounds. Lithium, beryllium, magnesium, zinc, manganese, cobalt and nickel may be used with particular advantage as the spinel-forming metals. Lithium spinel has proved to be very suitable. The spinel content of the support should amount to at least 20% and preferably to 40% and more. It has proved to be particularly advantageous to use supports of the kind which for the most part, i.e. up to 80-100% for example, consist of spinel in addition optionally to known lubricants or diluents. Among the various other ways of producing spinel-containing supports, it has proved particularly advantageous to start With highly active aluminium oxide in piece form, with an inner surface of from 200* to 350 m. /g. These pieces of aluminium oxide, for example in the form of tablets, pellets or spheres with average diameter dimensions of from 2 to 10 mm., may be impregnated with a solution of a compound (salt, hydroxide) of the spinel-forming metal to be used and then dried. Where salts are used for impregnation, they are advantageously converted into oxides by heating to 250-650 C., optionally in the presence of gases containing oxygen or steam. This is followed by heating, i.e. calcining, to 900-1300 C., for example for a period of from 1 to 10 hours, in order to perform the spinel formation. To obtain stoichiometric spinel formation, it is possible repeatedly to impregnate the alumina support with the particular solutions after intermediate drying and decomposition of the salts. One alternative to this is to start with finegrained aluminum oxide With a large inner surface and to add to it a solution of the metal compound, in which case the solution of the metal compound may be added from the outset in such a quantity as corresponds to the subsequent intended level of conversion into spinel. After drying and, optionally, roasting, the mass may be formed in the presence of lubricants for example into strands or pellets and calcined, as described above. In addition, it is possible to produce mixed spinels by using several spinel-forming metal compounds. The temperatures at which and the periods for which calcination is carried out differ from one type of spinel to the other, although it is readily possible by preliminary tests to determine the conditions to be maintained in order to obtain the required properties in the catalyst support. In particular, the calcination temperature and the calcination time affect the inner surface and the pore diameter of the support.

The noble metals may be applied to the supports in quantities of for example 0.05 to 5% by weight, advantageously 0.1 to 1% by weight. In cases Where palladium is used as the noble metal, the support is impregnated for example with an aqueous palladium salt solution and the palladium is deposited on to the support by reduction, for example with formaldehyde in alkaline solution. It is also possible, however, to convert the palladium from inorganic salt form, for example palladium nitrate, or from organic salt form, for example acetate, into the metal by reduction with hydrogen at elevated temperature.

In order to remove the unstable (diolefinic) compounds, the starting material is allowed to trickle in the liquid phase through vertical tubes over the catalyst fixedly arranged in the reaction zone, e.g. as a stationary catalyst bed. Tubes with internal diameters of from 25 to 60 mm., in particular 4060 mm., and lengths of from 3 to 8 meters, may be used to accommodate the catalyst.

In many cases, it is of advantage to arrange the two reaction zones in a single bundle of tubes. However, it is also possible to operate in two or more reactors arranged one behind the other, in which case the product from one zone is delivered to the head of the hydrogenation reactor of the next zone. In order to obtain a uniform distribution of the products in the following reactors also, it is advisable to separate gas from liquid in a separator following the preceding hydrogenation reactor, and to feed both to the next reactor separately from one another. At the same time, hydrogen is fed in from above. There is no need to use pure hydrogen, although the hydrogen-containing fraction, in addition to inert gases, should contain at least 50% by volume, as far as possible more than 70% by volume of hydrogen. It is advisable to use hydrogen pressures of from 20 to 80 atms., advantageously 30 to 60 atms. It is possible for example to operate in such a way that the temperature of the incoming pyrolysis gasoline amounts to between 20 and 30 C. and that the temperature in the first part of the reaction zone, i.e. in the diolefin hydrogenation section, does not exceed 100 C.

The temperature is then increased to above 100 C., e.g. about l50250 C., in the second part of the reaction zone. It is possible to control the temperature by surrounding the reaction tubes with heat-transfer agents divided up into two or more chambers, i.e. heating jackets, over the length of the reactor. Water for example may be used as the heat-transfer agent, being cycled through the chambers and an externally situated heat source, for example a heat exchanger. It is possible by virtue of this arrangement to ensure that in the first part of the reactor for example the temperature of the reactants leaving this first part of the hydrogenation remains below 70 C. to 100 C. preferably 95 C., i.e. below the temperature at which the unstable compounds are polymerised, and that, only after these unstable predominantly dioleiinic compounds have been hydrogenated in the first stage, the temperature is increased to such an extent that then most of the monoolefins also are hydrogenated in the second stage. The hourly throughput of pyrolysis gasoline amounts in the first hydrogenation stage to between 2 and 10, and preferably to between and 7.5 kg./litre of catalyst volume, and in the second stage to between 1 and 5, and preferably to between 2 and 3, kg./litre of catalyst volume.

The catalyst volume in the two sections 'will depend upon the loads prevailing. Between 0.2 and twice the volume of the already hydrogenated or part-hydrogenated product may be recycled from the separators to the head of the reactor(s) and mixed with the feed, for which purpose recycling is preferably carried out without release of pressure.

The quantity of hydrogen to be used is generally selected in such a way that it is from 10 to 30% higher than the amount of hydrogen absorbed by chemical bonding into the pyrolysis gasoline.

I The liquid products may be separated from the gaseous products in a separator arranged behind the reaction zone, whilst gas may be released from the gas zone in such quantities that the required excess of hydrogen is run off here. The extent of which the reaction product is cooled behind the reaction zone is governed by the requirements of stabilisation of the liquid hydrogenated product in a following stabilisation column.

The products of hydrogenation have a diene content of less than 1% by weight, usually less than 0.1% by weight. The gum contents before and after ageing are less than 5 mg./ ml., and the induction time for ageing is greater than 240 minutes. The bromine number is usually between 1 and 12 g./ 100 g. The octane numbers of the hydrogenation products with 0.04% by volume of lead tetraethyl (TEL) added thereto are substantially the same as the corresponding octane numbers of the starting materials. Accordingly, it is now possible through this procedure to hydrogenate most of the monoolefins without appreciably affecting the octane rating of the lead-containing gasoline. The procedure described is accompanied by some decomposition of the organic sulphur compounds present in the starting material. The sulphur content of the hydrogenation product leaving the second hydrogenation step is usually between 10 and 80% of the sulphur content of the starting materials. Accordingly, apart from the advantages accompanying removal of the olefins, the starting material is also desulphurized to an appreciable extent, which also contributes towards improving the lead susceptibility of the hydrogenated product 'with respect to the starting material. It is remarkable that, despite this information of hydrogen sulphide, the catalyst retains a satisfactory level of hydrogenation activity. As a result of tests lasting several months, it has been found that the aforementioned catalysts show an extremely constant level of hydrogenation activity.

EXAMPLE To prepare the catalyst support, 3-5 mm. diameter spheres of active aluminium oxide with an inner surface of 288 mF/g. were impregnated at room temperature with a solution of lithium formate and dried at C. The support was then calcined for 6 hours at 1050 C. The finished support contained 0.93% by weight of lithium, 75% consisting of lithium aluminium spinel and 25% of a-aluminium oxide. The inner surface measured 46 m. /g., and the average pore diameter 700 A.

To prepare the catalyst, the support was impregnated with a solution of palladium (ID-chloride. The palladium salt was reduced to palladium with alkaline formalin. The catalyst was then washed free of chlorine and dried. The finished catalyst had a palladium content of 0.6% by weight.

The catalyst was introduced into a vertically arranged tube 4 metres long with an internal diameter of 24 mm. in a quantity of 1.6 litres. Starting materials and gaseous hydrogen were fed in at the upper end. The two halves of the reactor tube were heated with water separately from one another.

Hydrogenation of the pyrolysis gasoline was carried out in a hydrogen atmosphere of 50 atms. The product to be hydrogenated, which had been redistilled beforehand, and to which 40 ppm. of di-tert.-butyl phenol had been added as an inhibitor, was introduced with the hydrogen at the upper end of the reactor at 25 C. under a load of 2 kg./ litre hour. The liquid product trickled down over the catalyst in the hydrogen atmosphere. In the upper half of the reactor, the temperature of the heating water amounted to 75 C., and in the lower half to 220 C., the temperature of the reaction product at the end of the reactor was 220 C.

The following table provides a comparison between the properties of two redistilled pyrolysis gasolines from mildand severe-cracking plants with those of the corresponding hydrogenation products obtained therefrom in accordance with the invention. The table also shows the results obtained from hydrogenation in accordance with the invention under the same conditions using a benzene/ toluene fraction of pyrolysis gasoline from short residence time cracking:

9. Process according to claim 8 wherein the support for the noble metal has an inner surface of substantially be- Hydrogenation Hydrogenation Fed benzcne- Hydrogenation product avge. product avge. toluene fraction product avgc. Fed cracked values from Fed cracked values from of a cracked values from gasoline from a 1,000 operating gasoline from 900 operating gasoline from 1,000 operating mild-cracking hours a severehours short residence hours 11 Odo Density at 20 C 0. 775 0. 768 0. 823 0. 817 0. 858 0. 853 Bromine number (g./100 g.) 65 7 73 5 40 3 Monoolefin content (percent by weight) Approx. 4 Approx. 3 Approx. 2 Diene content (percent by wiehgt) 18. 0 23. 8 0 13. 1 0 Gum content before ageing (mg. /100 ml.) 1 1 2 Gum content after ageing (mg/100 ml.)- 5, 300 1 8, 240 Induction time (mins.) 130 240 00 Research octane number (RON) unleaded 97. 0 93. 100. 0

.047 by volume tetraethyl lead (TEL) 101.0 99. 5 100. 5 Motor octane number (MON), unleaded 85. 0 82. 9 87. 0 MON-+0.04% by volume TEL r. 88.8 89. 1 89. 0 Benzene (percent by weight) 25. 2 25. l 43. 2 Toluene (percent by weight)..- 1G. 8 16. 8 17. 4 Sulphur (percent by weight) 0. 011 0. 007 0. 01

1 Deep yellow. 3 Unpleasant. 1 Colour-less. 4 Pleasantly aromatic.

What is claimed is: tween about 20-120 m. g. and an average pore diameter 1. Process for the hydrogenation of pyrolysis gasolines and fractions thereof which comprises hydrogenating a member selected from the group consisting of pyrolysis gasolines and fractions thereof in a first step at a temperature below about 100 C. in the presence of noble metal on an aluminum spinel support as hydrogenation catalyst for the selective hydrogenation substantially of the diolefins therein, and thereafter hydrogenating further the hydrocarbon mixture obtained from the first step in a second step at a temperature substantially between about 150-250" C. in the presence of the same catalyst as in the first step.

2. Process according to claim 1 wherein the second step hydrogenation is carried out directly after the first step hydrogenation in the same reactor, at the same pressure and with the identical catalyst.

3. Process according to claim 1 wherein the hydrogenation in both the first and secondsteps is carried out in a substantially static hydrogen atmosphere.

4. Process according to claim 3 wherein the hydro genation in each of the first and second steps is carried out at a hydrogen pressure substantially between about 20-80 atmospheres.

5. Process according to claim 3 wherein the hydrogen atmosphere contains at least 50% by volume of hydrogen, with the remainder being inert gas.

6. Process according to claim 5 wherein the quantity of used hydrogen is substantially between about 1030% higher than the amount being absorbed by chemical bonding.

7. Process according to claim 1 wherein substantially between about 0.2-2 parts by weight of hydrogenation product per part by weight of fresh feed are recycled to the inlet of the hydrogenation reactor.

8. Process according to claim 1 wherein lithium aluminum spinel is used as the support for the noble metal.

substantially between about 200-800 A.

10. Process according to claim 1 for the hydrogenation of pyrolysis gasolines and fractions thereof to reduce the olefin and organic sulfur content thereof which comprises hydrogenating a member selected from the group consisting of pyrolysis gasolines and fractions thereof in a first step at a temperature substantially below between about -95 C. in trickle phase in a substantially static hydrogen atmosphere at a hydrogen pressure substantially between about 20-80 atmospheres in the presence of noble metal on a lithium aluminum spinel as hydrogenation catalyst for the selective hydrogenation substantially of the diolefins contents therein, and thereafter hydrogenating further the hydrocarbon mixture obtained from the first step in a second step at a temperature substantially between about ISO-250 C. in trickle phase in a substantially static hydrogen atmosphere at a hydrogen pressure substantially between about 20-80 atmospheres in the presence of the same catalyst as in the first step for the further selective hydrogenation substantially of the mono-olefins and part of the sulfur content therein.

11. Process according to claim 10 wherein the pyrolysis gasoline feed is substantially free from constituents having boiling points above the boiling range of the pyrolysis gasoline feed.

References Cited UNITED STATES PATENTS 3,075,917 1/1963 Kronig et al. 208144 3,167,498 1/ 1965 Kronig et al. 260677H 3,182,015 5/1965 Kronig et al. 208-443 3,459,657 8/1969 Kronig et al. 260677 3,471,583 10/1969 Fleming 260677 HERBERT LEVINE, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,556,983 Dated January 19, 1971 Inventor(s) Walter Kronlg 12 a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Columns 5 and 6 Table Table headings: Column 1 after "cracking" insert plant column 2 aft "hours" insert (Invention) column 3, after "severe-" insert cracking plant column 4, after "hours" insert (Invention) column 5 after "residence" insert tim cracking column 6 after "hours" insert [Invention] Signed and sealed this 1st day of June 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER Attesting Officer Commissioner of Pat:

1 FORM Po-wso (10-69) 

